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Time to Take Low-Carb Diets Seriously?

Results from two randomized trials suggest yes.

In two randomized trials, researchers compared low-carbohydrate diets with low-fat diets to assess effects on cholesterol levels and weight loss.

In a 24-week study, 120 overweight, hyperlipidemic adults (mean BMI, 34) were randomized to eat a low-carbohydrate diet (starting at <20 g/day of carbs, plus nutritional supplements) or a low-fat diet (<30% of daily energy from fat, <300 mg of daily cholesterol, and intake of 500-1000 kcal/day less than usual). Both groups received exercise recommendations and support at group meetings. The retention rate was significantly higher in the low-carb group than in the low-fat group (76% vs. 57%). By 24 weeks, low-carb dieters had fared significantly better than low-fat dieters in mean weight loss (–12.0 kg vs. –6.5 kg), triglyceride change (–74 mg/dL vs. –28 mg/dL), and HDL change (+5.5 mg/dL vs. –1.6 mg/dL); LDL changes were similar in the two groups.

In another study (a 1-year follow-up of previously reported 6-month results; Journal Watch Cardiology Aug 8 2003), 132 severely obese adults (mean BMI, 43; about half with hyperlipidemia, about 40% with diabetes) were randomized to eat a low-carb diet (30 g/day of carbs) or a conventional calorie- and fat-restricted diet (intake of 500 kcal/day less than usual, 30% of calories from fat). Both groups received support at group meetings. At 1 year, the low-carb and low-fat groups did not differ significantly in retention rates (69% and 63%) or mean weight loss (–5.1 kg and –3.1 kg). However, low-carb dieters fared significantly better than low-fat dieters in changes in mean triglyceride levels (–58 mg/dL vs. +4 mg/dL), HDL (–1 mg/dL vs. –5 mg/dL), and hemoglobin A_1C (–0.7% vs. –0.1%); LDL changes were similar in the two groups.

Comment: Results from these studies should mitigate concerns about adverse lipid effects of low-carbohydrate diets, and even suggest some benefit. Some caveats are that dropout rates were high (particularly among low-fat dieters in the shorter study), dietary adherence was suboptimal, and (in the longer study) 6-month weight-loss advantages in the low-carb group eventually were reduced. Nevertheless, one can no longer dismiss low-carbohydrate dieting as fad. An editorialist recommends encouraging overweight patients to engage in regular physical activity and to experiment with various diets, including low-carb, with an emphasis on healthy sources of fat and protein.

— Joel M. Gore, MD

Published in Journal Watch Cardiology July 9, 2004

Citation(s):

Yancy WS Jr et al. A low-carbohydrate, ketogenic diet versus a low-fat diet to treat obesity and hyperlipidemia: A randomized, controlled trial. Ann Intern Med 2004 May 18; 140:769-77.

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• Medline abstract (Free)

Stern L et al. The effects of low-carbohydrate versus conventional weight loss diets in severely obese adults: One-year follow-up of a randomized trial. Ann Intern Med 2004 May 18; 140:778-85.

• Original article (Subscription may be required)
• Medline abstract (Free)

Willett WC. Reduced-carbohydrate diets: No roll in weight management? Ann Intern Med 2004 May 18; 140:836-7.

• Original article (Subscription may be required)
• Medline abstract (Free)